This invention relates to a method of treatment of a photo mask such as the inspection and retouching thereof. More particularly, it relates to a method of inspecting the presence of defects in a mask pattern by irradiating the photo mask with an electron beam, and a method of retouching the defects of the mask pattern found by such an inspection. It also relates to a photo mask structure for use in the treatment.
The surface of a photo mask is irradiated with an electron beam for the purpose of inspecting the mask pattern of the photo mask. One of difficulties encountered in that case is the charge-up phenomenon of the photo mask attributed to electrons which have entered the photo mask. FIG. 1 shows the sectional structure of a photo mask which has heretofore been generally employed. Although light interceptive parts 3 and 3' are often formed of a conductive material such as chromium (Cr), a transparent glass substrate 1 itself is an insulator. Therefore, electrons having entered the light interceptive part 3 in the form of an island or an exposed glass part (transparent part) 5 cannot escape or flow. When an electron beam impinges on such a mask, the surface of the mask is charged negatively, and electrons to subsequently enter are repelled. For this reason, it is extremely difficult to precisely inspect the mask pattern.
On the other hand, in case of retouching the defects of a mask pattern in a photo mask, the defects need to be precisely examined and recognized. As understood from the above description, however, it is difficult to perform an accurate retouching for the mask pattern which is very fine.